Vertical tube module once-through steam generator



Dec. 12, 1967 M. R. WiLLIAMSON ETAL 3,

VERTICAL TUBE MODULE ONCE-*THROUGH STEAM GENERATOR Filed Sept. 50, 1965 United States Patent 3,357,409 VERTICAL TUBE MODULE ONCE-THROUGH STEAM GENERATOR Malcolm Richard Williamson, Oldham, and Michael Joseph Chamberlain, Hadlow, near Tonbridge, England, assignors to United Kingdom Atomic Energy Authority, London, England Filed Sept. 30, 1965, 'Ser. No. 491,732 Claims priority, application Great Britain, Oct. 7,

This invention relates to improvements in or relating to vapour generators and is especially concerned with once-through steam generators which find particular application in integrated nuclear reactor steam generator systems.

The invention will be described with reference to steam generation but it is to be noted that references to water and steam are intended to include references to any liquid and its vapour unless the context specifically re quires otherwise.

In an integrated nuclear reactor steam generator system. the core and steam generator are both contained within the reactor pressure vessel. Generally the core, in which the primary fluid is heated, is situated in the lower part of an upright cylindrical pressure vessel, and the steam generator is situated above the core in an annular chamber in a higher part of the pressure vessel. The primary fiuid is circulated from the core to the steam generator and then back to the core again. Because the steam generator is within the pressure vessel its height is limited and it is therefore difiicult to obtain a good quality steam without passing it several times in heating contact with the primary fiuid.

In accordance with the invention there is provided a steam generator in which the heating surface comprises a number of similar once-through tube clusters exposed to a heating fiuid, each cluster including a number of tubes extending between headers and assembled into a multipass arrangement within the cluster, so that water can be fed to the clusters and removed as superheated steam.

A steam generator having its heating surface planned in this way gives superheated steam in the limited height ordinarily available in the pressure vessel, with single once-through how: that is to say it is not necessary to provide separate tube banks for preheating, evaporating and superheating or to cause the water and steam to flow through a succession of different fiow paths in different tube banks. This steam generator can be used in other applications besides integrated nuclear steam generator sys ems.

In the preferred arrangement, each tube cluster is a threepass cluster, with preheating, evaporating and superheating. respectively, taking place in the three passes.

Each tube cluster may comprise a number of straight tubes which are welded between small headers. The crosssectional shape of each cluster may, with advantage, be hexagonal so that the clusters can be arranged side by side to form a honeycomb pattern, although other regular or irregular polygonal cross-sectional shapes are possible. The best cross-sectional shape is usually that which enables a maximum number of clusters to be fitted within the annular chamber so as to provide the largest possible surface. Also the tubes should be spaced as uniformly as possible over the crosssectional area of the generator.

In one advantageous arrangement, the tube cluster comprises a central tube down which the feed water is directed. The feed water is preheated in this tube but is preferably not raised to boiling temperature so as to avoid ditficu ties with boiling since the water is being fed downwardly. Upon emerging from this tube the water is directed by a flow divider upwardly through a number of ice achieved and the steam is superheated. The relative numbers of evaporator and superheater tubes is chosen so as to give the optimum heat transfer in any particular design. An example of a steam generator in accordance with the invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 is a longitudinal axial section through an integrated nuclear reactor steam generator system;

FIGURE 2 is a longitudinal axial section through a tube cluster of the steam generator; and

FIGURE 3 is a section taken on the line 33 of FIGURE 2.

The integrated nuclear reactor steam generator system shown'in FIGURE 1 comprises an upright cylindrical pressure vessel 1 containing a core 2 and a steam generator 3. The steam generator is positioned within an annular chamber 4 in the vessel. Primary fluid is circulated through the core 2. upwardly through an inner annular chamber 5, downwardly through the annular chamber 4,and is then collected in a lower annular chamber 6. From this chamber 6 the primary fluid is withdrawn through a tube 7 passing out of the pressure vessel 1, fed to a circulating pump (not shown), and then returned to the core 2 through a tube 8 concentrically surrounding the tube 7.

The steam generator 3 comprises a number of tube clusters 9 which are fed with feed water from an inlet tube 10, and from which superheated steam is withdrawn through an outlet tube 11 concentrically surrounding'the tube 10. By providing concentric inlet and outlet tubes the steam generator only requires a single hole to be made in the pressure vessel 1.

. As best shown in FIGURES 2 and 3 each tube cluster 9 comprises a number of upright straight tubes welded between an upper header 12 and a lower header 13. Each cluster has a central preheater tube 14 which passes through the upper header 12 and which is connected to the lower header 13. The central tube communicates with a chamber 15 in the lower header l3 and this chamber 15 is arranged to direct the how of heated Water from the tube 14 into evaporator tubes 16 which also communicate with the chamber 15. In the steam generator shown in the drawings, twelve evaporator tubes 16 are provided and these surround the central tube 14. The evaporator tubes 16 communicate with the upper header 12 and also leading from the upper header 12 are superheater tubes 17. Six superheater tubes 17 are provided in the steam generator shown in the drawings and at their lower ends these tubes 17 communicate with the lower header 13.

The feed water is led to each cluster 9 through inlet tubes 18 communicating with the tubes i0 and 14 and superheated steam is removed from the lower headers 13 by tubes 19 which communicate with the outlet tube 11.

As best shown in FIGURE 3 the cross-sectional arrangement of the tubes 14, 16 and 17 is hexagonal, and it will be appreciated that this cross-sectional shape allows the clusters 9 to be arranged side by side to form a honeycomb structure. In this way a relatively large heating surface is provided in a relatively small space.

Each of the tubes 14, 16 and 17 has an inner spiral turbulator so as to give a better heat transfer between the heating fluid and the water or steam.

In operation the primary fluid is heated in the core and is then circulated past the tubes 14, 16 and 17 where it is cooled. It is then recirculated so as to be reheated in the core. Feed water is fed to the tube clusters 9 through the inlet tubes and 18 and the feed water passes downwardly through the central tube 14. In this plete evaporation of the water and then superheating of the steam are achieved. The tubes 17 feed the superheated steam into the lower header 13 from whenceit is removed through the outlet tubes 19 and 11.

In order to overcome, or at least reduce, flow instability in the tube clusters, each perheater tube 14 is provided with a spiral turbulator which is more closely wound than is necessary simply for heat transfer. This provides a relatively large pressure drop and thus reduces the influence of any uneven flow distribution occurring between clusters. Also the presence of the upper header 12 reduces any flow instability arising through oscillations produced by the boiling in the evaporator tubes 16, since in this header such vibrations are taken up or buffered.

We claim:

1. A steam generator comprising a cluster of oncethrough tubes the external surfaces of which are exposed to a heating fluid and including an upper header and a lower header, said lower header including a first chamber and a second chamber, means including at least one of said tubes for feeding water to the said first chamber, at least some of said tubes of said cluster being evaporator tubes extending from said first chamber to said upper header wherein water evaporates as it passes upwardly through said evaporator tubes from said first chamber to said upper header, and at least some of said tubes of said cluster being superheater tubes extending from said upper header to said second chamber wherein the water evaporated in the said evaporating tubes is superheated as it passes downwardly through said superheater tubes from said upper header to said second chamber, and an outlet for superheated steam connected to said second chamber. 9

2. A steam generator according to claim 1, in which the said tube included in the means for feeding water to the said first chamber comprises a preheater tube extending through the upper header and externally of the evaporator and superheater tubes to the said first chamber, and wherein cedwater passes downwardly through said preheatcr tube to said first chamber.

3. A steam generator according to claim 2 in which the said tubes are arranged in a bundle and wherein a single preheater tube occupies a central position in said bundle, and said evaporator and superheater tubes are disposed about said preheater tube, said superheater tubes occupying positions at the outer periphery of the bundle.

4. An integrated nuclear reactor including a pressure vessel having mounted therein a core, a steam generating system and a means for circulating a primary coolant from said core to said steam generating system, said steam generating system including a plurality of similar once-through tube clusters exposed to said primary coolant, each of said clusters including an upper header and a lower header, said lower header including a first chamber and a second chamber, means including at least one of said tubes for feeding water to the said first chamber,

at least some of said tubes of said cluster being evaporator tubes extending from said first chamber to said upper header wherein water evaporates as it passes upwardly through said evaporator tubes from said first chamber 'to said upper header, and at least some of said tubes. of

said cluster being superheater tubes extending from said upper header to said second chamber wherein the water evaporated in the said evaporating tubes is superheated as it passes downwardly through said superheater tubes from said upper header to said second chamber. and an outlet for superheated steam connected to said second chamber.

5. A generator according to claim 1, in which each tube has a spiral turbulator within it.

6. A generator according to claim 1, in which the crosssectional shape of the cluster is hexagonal.

References Cited UNITED STATES PATENTS 3,018,764 l/l962 Huet 122-34 3,097,630 7/1963 Kinyon et al 122-34 3,104,652 9/1963 Tillequin et al. 12232 3,195,517 7/1965 Bell 122-406 3,267,907 8/1966 Glausser et al. 122-34 FOREIGN PATENTS 865,997 4/1961 Great Britain.

KENNETH w. SPRAGUE, Primary Examiner. 

1. STEAM GENERATOR COMPRISING A CLUSTER OF ONCETHROUGH TUBES THE EXTERNAL SURFACES OF WHICH ARE EXPOSED TO A HEATING FLUID AND INCLUDING AN UPPER HEADER AND A LOWER LADDER, SAID LOWER HEADER INCLUDING A FIRST CHAMBER AND A SECOND CHAMBER, MEANS INCLUDING AT LEAST ONE OF SAID TUBES FOR FEEDING WATER TO THE SAID FIRST CHAMBER, A LEAST SOME OF SAID TUBES OF SAID CLUSTER BEING EVAPORATOR TUBES EXTENDING FROM SAID FIRST CHAMBER TO SAID UPPER HEADER WHEREIN WATER EVAPORATES AS IT PASSES UPWARDLY THROUGH SAID EVAPORATOR TUBES FROM SAID FIRST CHAMBER TO SAID UPPER HEADER, AND AT LEAST SOME OF SAID TUBES OF SAID CLUSTER BEING SUPERHEATER TUBES EXTENDING FROM SAID UPPER HEADER TO SAID SECOND CHAMBER WHEREIN THE WATER EVAPORATED IN THE SAID EVAPORATING TUBES IN SUPERHEATED 